This Section combines molecular and neuroanatomical methods to reveal dynamic CNS events that relate to issues of mental health and drug abuse. Mapping drug and neuro-transmitter receptors using autoradiography has provided important basic information about brain organization and function. The cannabinoid receptor has been localized to specific neuronal elements in brain, and we examined its relationship to the dopamine system and to "reward" pathways. In situ hybridization histochemistry is used to examine the regulation of gene expression of neuropeptides, monoamine transporters and synthe-sizing enzymes, and adrenal steroid receptors. Studies are designed to elucidate brain mechanisms involved in stress and chronic antidepressant drug treatment, with a focus on the role of corticotropin releasing hormone in the pathophysiology of affective disorders. Other studies examine CNS adaptive changes caused by drugs of abuse, such as marijuana and cocaine.